The present invention relates to newly identified human sulfatases. In particular, the invention relates to sulfatase polypeptides and polynucleotides, methods of detecting the sulfatase polypeptides and polynucleotides, and methods of diagnosing and treating sulfatase-related disorders. Also provided are vectors, host cells, and recombinant methods for making and using the novel molecules.
The biology and functions of the reversible sulfation pathway catalyzed by human sulfotransferases and sulfatases has been reviewed by Coughtrie et al. (Chemico-Biological Interactions 109: 3-27 (1998)). This review, summarized below, focuses on the sulfation of small molecules carried out by cytosolic sulfotransferases rather than the sulfation of macromolecules and lipids catalyzed by membrane-associated sulfotransferases.
Sulfation functions in the metabolism of xenobiotic compounds, steroid biosynthesis, and modulating the biological activity and inactivation and elimination of potent endogenous chemicals such as thyroid hormones, steroids and catechols. This pathway is reversible, comprising the sulfotransferase enzymes that cause the sulfation and the sulfatases that hydrolyze the sulfate esters formed by the action of the sulfotransferases. Accordingly, the interplay between these families regulates the availability and biological activity of xenobiotic and endogenous chemicals. The sulfatases, including the arylsulfatases (ARS), are located in lysosomes or endoplasmic reticulum.
The presence of sulfated components depends upon the availability of key members of the sulfate pathway, i.e., substrate and activated sulfate donor molecule (co-substrate) and the balance between sulfation and sulfate conjugate hydrolysis that depends upon the activity and localization of the sulfotransferases and the sulfatases. Essentially, divalent sulfate is converted to adenosine 5xe2x80x2 phosphosulfate (PAPS) by hydrolysis of ATP. This compound is in turn converted to 3xe2x80x2 phosphoadenosine 5xe2x80x2 phosphosulfate by hydrolysis of ATP to ADP. This compound is then converted to adenosine 3xe2x80x2 5xe2x80x2 biphosphate concurrently with the formation of 4-nitrophenolsulfate from 4-nitrophenol. An ARS would then cleave the monovalent sulfate from the 4-nitrophenolsulfate to produce the original 4-nitrophenol. This forms the basis for the sulfation system in humans. Over- or under-production of any of these key molecules can result in sulfate-related disorders. For example, the brachymorphic mouse has a connective tissue disorder that results from a defect in PAPS formation that causes undersulfated cartilage proteoglycans.
ARS enzymes and their genes have been associated with specific genetic diseases. ARSA is located in the lysosomes and removes sulfate from sulfated glycolipids. A deficiency of ARSA has been associated with metachromatic leukodystrophy and multiple sulfatase deficiency (MSD). ARSB is located in lysosomes and has, as an endogenous substrate, dermatan sulfate and chondrotin sulfate. A deficiency of ARSB is associated with Maroteaux-Lamy syndrome and MSD. ARSC is located in the endoplasmic reticulum and has, as its endogenous substrate, cholesterol sulfate and steroid sulfates. A deficiency of ARSC is associated with X-linked ichthyosis and MSD. ARSD may be associated with MSD. ARSE has been associated with chondrodysplasia punctata and MSD. ARSF may be associated with MSD. ARSC hydrolyses sulfate esters on a wide range of steroids and cholesterol. ARSs also hydrolyse sulfate conjugates of xenobiotics.
MSD results from an inability to perform a co- or post-translational modification of a cysteine residue to serine semialdehyde (2-oxo-3-propionic acid). This residue is conserved in all eukaryotic sulfatases described by Coughtrie et al. ARSC may have a very broad specificity, extending to iodothyronine sulfates and a number of sulfate conjugates of xenobiotic phenols.
The kinetic and catalytic properties of ARS enzymes in isolation, important for understanding substrate specificity and the physical and chemical properties of enzymes and substrates that allow substrate preference, have been characterized recently based on recombinant enzyme systems. For the expression of the human sulfotransferases, COS and V79 cells have been used. Coughtrie et al. have constructed and characterized V79 cell lines stably expressing ARSA, ARSB, and ARSC. These cell lines exhibited the expected substrate preferences of the three enzymes among the substrates 4-nitrocatechol sulfate, estrone sulfate, and dehydroepiandrosterone sulfate(DHEAS).
The sulfation of small molecules can be broadly divided into the areas of chemical defense, hormone biosynthesis, and bioactivation. It was originally viewed that sulfation protected against the toxic effects of xenobiotics in that sulfate conjugates are more readily excreted in urine or bile and generally exhibit reduced pharmacological/biological activity relative to the parent compound. Many drugs and other xenobiotics are conjugated with sulfate. Many phenolic metabolites of the cytochrome P450 mono-oxygenase system are excreted as sulfate conjugates.
Further, potent endogenous chemicals, such as steroids and catecholamines are found at high levels as circulating sulfate conjugates. For example, greater than 90% of circulating dopamine exists as the sulfated form. Sulfation is also suggested to play a role in the inactivation of potent steroids such as estrogens and androgens. Accordingly, sulfation is important in metabolism and homeostasis of such compounds in humans. DHEAS is the major circulating steroid in humans and estrone sulfate is the major estrogen. These chemicals act as precursors of estrogens and androgens. Extremely large quantities of such steroids or estrogens may occur during various stages of development, such as pregnancy. Estrone sulfate is a precursor for xcex2-estradiol synthesis. In breast cancer cells it is hydrolysed by steroid sulfatase (ARSC) to estrone which is then converted to xcex2-estradiol by action of another enzyme. Accordingly, ARSC is important for maintaining active estrogen. It is thus an important therapeutic target for the treatment of breast cancer.
Cholesterol sulfate, synthesized in the skin epidermis, may have a role in keratinocyte differentiation. Accordingly, hydrolysis of cholesterol sulfate by steroid sulfatase may be important in skin formation and differentiation. This is the major organ affected in X-linked ichthyosis caused by mutations in ARSC.
Although sulfation may widely serve to detoxify potent compounds, some sulfate conjugates are more biologically active than the corresponding parent compound. Minoxidil and cicletanine are activated upon sulfation. Further, an inhibitor of ARSC was shown to potentiate the memory enhancing effect of DHEAS. This suggests a role for sulfates and sulfation in the central nervous system.
An important example of bioactivation by means of sulfation, however, occurs with dietary and environmental mutagens and carcinogens. For a large number of these, sulfation is the terminal step in the pathway to metabolic activation. Examples of such chemicals include aromatic amines (including heterocyclic amines) and benzylic alchohols of chemicals such as polycyclic aromatic hydrocarbons, safrole, and estragole.
The sulfatase gene family has been reviewed in Parenti et al. (Current Opinion in Genetics and Development 7:386-391(1997)), summarized below.
The sulfatase family of enzymes is functionally and structurally similar. Nevertheless, these enzymes catalyze the hydrolysis of sulfate ester bonds from a wide variety of substrates ranging from complex molecules such as glycosaminoglycans and sulfolipids to steroid sulfates (see also Coughtrie et al., above). Several human genetic disorders result from the accumulation of intermediate sulfate compounds that result from a deficiency of single or multiple sulfatase activities. A subset of sulfatase, ARS, is characterized by the ability to hydrolyze sulfate esters of chromogenic or fluorogenic aromatic compounds such as p-nitrocatechol sulfate and 4-methylumbelliferyl sulfate. Desulfation is required to degrade glycosaminoglycans, heparan sulfate, chondroitin sulfate and dermatan sulfate and sulfolipids. Steroid sulfatase differs from other members of the family with respect to subcellular localization. It is localized in the microsomes rather than in lysosomes. Further, ARSD, ARSE, and ARSF are also non-lysosomal, being localized in the endoplasmic reticulum or Golgi compartment.
The natural substrate of ARSA is cerebroside sulfate. Associated diseases are MLD and MSD. The natural substrate of ARSB is dermatan sulfate. The disease associated with this enzyme is MPSVI and MSD. The natural substrate of ARSC/STS is sulfated steroids. Diseases associated with this enzyme are XLI and MSD. The natural substrates of ARSD-F are unknown. The natural substrates of iduronate-2-sulfate sulfatase (IDS) are dermatan sulfate and herparan sulfate. Diseases associated with this enzyme are MPSII and MSD. The natural substrate of galactose 6-sulfatase is keratan sulfate and chondroitin 6-sulfate. Diseases associated with this enzyme include MPSIVA and MSD. The natural substrate of glucosamine-6-sulfatase is heparan sulfate and keratan sulfate. A disease associated with this enzyme is MPSIIID and MSD. The natural substrate of glucuronate-2-sulfatase is heparan sulfate. The natural substrate of glucosamine-3-sulfatase is heparan sulfate.
Sulfatases are activated through conversion of a cysteine residue as described above. The conversion is required for catalytic activity and is defective in MSD. It is likely that all sulfatases undergo the same modification. The substitution of this cysteine was shown to destroy the enzymatic activity of N-acetyl galactosamine-4-sulfatase (ARSB). It has been shown that the modified residue and a metal ion are located at the base of a substrate binding pocket.
Nine human sulfatase genes are known and murine rat, goat, or avian orthologs for some of these have been identified. A high degree of similarity occurs particularly in the amino terminal region which contains accordingly a potential consensus sulfatase signature.
Sulfatases, as discussed above, are associated with human disease. Most sulfatase deficiencies cause lysosomal storage disorders. The mucopolysaccharidoses contain various associations of mental retardation, facial dysmorphisms, skeletal deformities, hepatosplenomegaly, and deformities of soft tissues caused by deficiencies of sulfatases acting on glycosaminoglycans. In metachromatic leukodystrophy, a deficiency of ARSA causes the storage of sulfolipids in the central and peripheral nervous systems, leading to neurologic deterioration. X-linked icythyosis is caused by STS deficiency leading to increased cholesterol sulfate levels. MSD, a disorder in which all sulfatase activities are simultaneously defective, was shown to result from a defect in the co- or post-translational processing of sulfatases.
Accordingly, sulfatases are a major target for drug action and development. Therefore, it is valuable to the field of pharmaceutical development to identify and characterize previously unknown sulfatases. The present invention advances the state of the art by providing previously unidentified human sulfatases.
Novel sulfatase nucleotide sequences, and the deduced sulfatase polypeptides are described herein. Accordingly, the invention provides isolated sulfatase nucleic acid molecules having the sequences shown in SEQ ID NOS:2, 4, 6, and 8 or in the cDNA deposited with ATCC as Patent Deposit Number PTA-1639 (which corresponds with SEQ ID NO:4), or PTA-1846 (which corresponds with SEQ ID NO:6) (xe2x80x9cthe deposited cDNAxe2x80x9d), and variants and fragments thereof.
It is also an object of the invention to provide nucleic acid molecules encoding the sulfatase polypeptides, and variants and fragments thereof. Such nucleic acid molecules are useful as targets and reagents in sulfatase expression assays, are applicable to treatment and diagnosis of sulfatase-related disorders and are useful for producing novel sulfatase polypeptides by recombinant methods.
The invention thus further provides nucleic acid constructs comprising the nucleic acid molecules described herein. In a preferred embodiment, the nucleic acid molecules of the invention are operatively linked to a regulatory sequence. The invention also provides vectors and host cells for expressing the sulfatase nucleic acid molecules and polypeptides, and particularly recombinant vectors and host cells.
In another aspect, it is an object of the invention to provide isolated sulfatase polypeptides and fragments and variants thereof, including a polypeptide having the amino acid sequence shown in SEQ ID NOS:1, 3, 5 or 7 or the amino acid sequences encoded by the deposited cDNAs. The disclosed sulfatase polypeptides are useful as reagents or targets in sulfatase assays and are applicable to treatment and diagnosis of sulfatase-related disorders.
The invention also provides assays for determining the activity of or the presence or absence of the sulfatase polypeptides or nucleic acid molecules in a biological sample, including for disease diagnosis. In addition, the invention provides assays for determining the presence of a mutation in the polypeptides or nucleic acid molecules, including for disease diagnosis.
A further object of the invention is to provide compounds that modulate expression of the sulfatase for treatment and diagnosis of sulfatase-related disorders. Such compounds may be used to treat conditions related to aberrant activity or expression of the sulfatase polypeptides or nucleic acids.
The disclosed invention further relates to methods and compositions for the study, modulation, diagnosis and treatment of sulfatase related disorders. The compositions include sulfatase polypeptides, nucleic acids, vectors, transformed cells and related variants thereof. In particular, the invention relates to the diagnosis and treatment of sulfatase-related disorders including, but not limited to disorders as described in the background above, further herein, or involving a tissue shown in the figures herein.
In yet another aspect, the invention provides antibodies or antigen-binding fragments thereof that selectively bind the sulfatase polypeptides and fragments. Such antibodies and antigen binding fragments have use in the detection of the sulfatase polypeptide, and in the prevention, diagnosis and treatment of sulfatase related disorders.
The sulfatases disclosed herein are designated as follows: 22438, 23553, 25278, and 26212.